This invention relates to windmills.
With the depletion of the world's mineral resources alternative sources of energy have become more popular and one of these is wind power. It has been proposed to erect large windmills having wind drive blades connected with generators for producing electricity. However, the large variations in wind speed have necessitated the incorporation of pitch variation for the blades so that a generally constant blade rotation is approximated.
GB-A-2,169,663, in the name of the present applicant, discloses a construction for a windmill blade wherein the blade is connected to a hub by means of an intermediate portion, the intermediate portion being connected to the hub and to the blade by first and second parallel hinges and being itself hinged along a third axis extending diagonally between the parallel hinges. The hub, blade and intermediate portion are moulded integrally from plastics material, the hinges comprising resilient creases in the plastic. In a rest condition, the creases orient the blade at an angle to its plane of rotation and rotation of the blade creates a centrifugal force on the blade which tends to flatten out the hinge creases, thereby reducing the pitch angle of the blade in response to changes in its speed of rotation caused by variations in wind speed.
The blade of GB-A-2,169,663 thus reacts automatically to changes in wind speed by reducing its pitch angle as the wind speed increases and increasing its pitch angle as the wind speed drops. However, it is not responsive to variations in the torsional loading on the shaft which it is driving, i.e. at any given wind speed the pitch angle will not change in response to changes in torque at the shaft.